This invention relates to an improvement on a fluid coupling for transmitting a rotating torque of a prime mover.
A fluid coupling has been used as a power transmission coupling for ships, industrial machinery, and automobiles. The fluid coupling comprises a pump having an annular pump shell, and a plurality of impellers disposed radially in the pump shell; and a turbine which has an annular turbine shell, and a plurality of runners disposed radially in the turbine shell and which is disposed opposite the pump. A working fluid is filled into the pump and the turbine. The so constituted fluid coupling has the pump connected to a crankshaft (an input shaft of the fluid coupling) of, for example, a diesel engine as a prime mover, and has the turbine attached to an output shaft disposed coaxially with the input shaft. There is also used a fluid coupling in which annular core rings for arranging the flow of the working fluid are provided in the pump shell and the turbine shell.
FIG. 6 shows the relationship between different revolution speeds of the input and output shafts and output torques (transmitted torques) in fluid couplings. In FIG. 6, a dashed line represents the torque transmission characteristics of a conventional fluid coupling. When a fluid coupling with such characteristics is installed in a driving device of a vehicle, the fluid coupling has a drag torque because of its characteristics, if the vehicle is at a stop, the engine is driven, and the transmission gear of a transmission is in mesh, namely, if the input shaft is rotated, while the output shaft is stopped. The drag torque generally refers to a transmitted torque when the engine is run at an idle speed (e.g., 500 rpm). This drag torque considerably increases, if the design point for the fluid coupling is set at a revolution speed ratio giving maximum efficiency, i.e., a pump-turbine revolution speed ratio in the range of from about 0.95 to 0.98. At a high drag torque, idle running of the engine is markedly unstable, and the unstable revolutions cause abnormal vibrations to a drive system. The high drag torque is also the cause of deteriorated fuel economy during idling.
As a measure for reducing the above-described drag torque, it is known to dispose a baffle plate between the pump and the turbine. The drag torque reducing measure using the baffle plate will be described with reference to FIGS. 7(a), 7(b) and 8. A fluid coupling shown in FIGS. 7(a) and 7(b) has an annular baffle plate BP disposed between a pump P and a turbine T and attached to an output shaft OS. A fluid coupling shown in FIG. 8 has an annular baffle plate BP disposed in an outer peripheral portion of a pump P.
In the fluid coupling shown in FIGS. 7(a) and 7(b), a working fluid given a rotational force by revolutions of the pump P at a low revolution speed flows into the turbine T from the outer peripheral side under a centrifugal force, as shown in FIG. 7(a). The working fluid that has driven the turbine T diminishes in the centrifugal force, approaches a core ring, and flows into the pump P. At a low revolution speed, therefore, the baffle plate BP disposed between the pump and the turbine exerts minimal effect, and cannot decrease the aforementioned drag torque. At a high revolution speed, the working fluid given a rotational force by revolutions of the pump P shown in FIG. 7(b) flows into the turbine T from the outer peripheral side under a centrifugal force. However, the working fluid flowing into the turbine T has a strong centrifugal force, and flows along the inner surface of the turbine shell. Thus, the working fluid contacts the baffle plate BP when entering the pump P. During high-speed revolutions, therefore, the baffle plate BP acts conspicuously, decreasing the transmitted torque (coupling efficiency). The torque transmission characteristics of the fluid coupling illustrated in FIGS. 7(a) and 7(b) are indicated by a one-dot chain line in FIG. 6. As discussed here, the fluid coupling shown in FIGS. 7(a) and 7(b) is a low efficiency coupling which not only is unable to reduce the drag torque that should be decreased at a low revolution speed, for example, during idle running of the engine, but also decreases the transmitted torque (coupling efficiency) at a high revolution speed. This problem is pronounced in a fluid coupling having core rings provided in the pump shell and the turbine shell.
The fluid coupling shown in FIG. 8, on the other hand, can reduce a drag torque at a low revolution speed, because the annular baffle plate BP is disposed in the outer peripheral portion of the pump P. However, this fluid coupling drastically decreases a transmitted torque at a high revolution speed. The torque transmission characteristics of the fluid coupling illustrated in FIG. 8 are indicated by a two-dot chain line in FIG. 6. That is, the working fluid given a rotating force by rotations of the pump P flows beside the outer periphery under a centrifugal force. However, when flowing out of the pump P at a peak flow velocity, the working fluid collides with the baffle plate BP to decline in flow velocity, and then flows into the turbine T. Thus, the transmitted torque (coupling efficiency) is sharply decreased during high speed rotations.
The object of the present invention is to provide a fluid coupling capable of effectively reducing a drag torque without decreasing a transmitted torque.
According to the invention, designed to attain the above object, there is provided a fluid coupling comprising:
a pump including a pump shell having an annular core ring, and a plurality of impellers disposed in the pump shell; and
a turbine including a turbine shell disposed opposite the pump and having an annular core ring, and a plurality of runners disposed in the turbine shell, wherein:
an annular baffle plate is mounted on an inner periphery of the core ring of the pump shell at an end portion of the core ring of the pump shell opposed to the turbine.
According to the invention, there is also provided the same fluid coupling, wherein:
an annular baffle plate is mounted on an outer periphery of the core ring of the pump shell at an end portion of the core ring of the pump shell opposed to the turbine.
According to the invention, there is also provided the same fluid coupling, wherein:
an annular baffle plate is mounted on an inner periphery of the core ring of the turbine at an end portion of the core ring of the turbine opposed to the pump shell.
According to the invention, there is also provided the same fluid coupling, wherein:
an annular baffle plate is mounted on an outer periphery of the core ring of the turbine at an end portion of the core ring of the turbine opposed to the pump shell.